General and practical synthesis of naphtho[2,1-d]oxazoles from naphthols and amines

A general and practical synthesis of naphtho[2,1-d]oxazoles from readily available naphthols and amines is developed using TEMPO as the oxygen source with outstanding functional group tolerance, especially for the construction of the naphthoxazole-related bioactive molecule PBNI and naphthoxazole-doped materials, as well as the polyaryloxazole-related ADN derivative. This protocol allows the rapid assembly of a small library of naphtho[2,1-d]oxazole skeletons (55 examples) that are difficult to be prepared by other methods. The electron paramagnetic resonance (EPR) and 18O-labeled experiments indicate that the radical adducts of TEMPO with naphthalenone radicals may serve as key intermediates.